1. Field of the Invention
The present invention relates to a double sided optical disc and a method for producing the double sided optical disc in which a first record carrier is united to a second record carrier so that each surface can be used as a signal recording surface and can be optically recorded and reproduced.
This application claims priority of Japanese Patent Application No. 2003-180024, filed on Jun. 24, 2003, the entirety of which is incorporated by reference herein.
2. Description of the Related Art
As an optical disc for recording and reproducing information by irradiating the optical disc with a laser beam, various kinds of media such as a read-only type compact disc (CD-DA, CD-ROM), a write-once type compact disc (CD-R), a rewritable type compact disc (CD-RW), etc. may be exemplified. Each of the discs is made of a base board having a diameter of 120 mm and the thickness of about 1.2 mm and is designed to be recorded and reproduced by a laser beam of substantially 780 nm.
Further, as the optical disc, there is a digital versatile disc (DVD) as well as the compact disc. In this DVD, one moving picture can be stored in the disc having the same diameter of 120 mm as that of the compact disc with an image quality similar to that of a present television. The DVD needs to increase a storage capacity to six to eight times as high as that of the compact disc. Thus, the DVD records and reproduces data by using a laser beam having the wavelength of 635 to 650 nm shorter than the laser beam used for the compact disc or the like. While the compact disc is made of a single board, the DVD is formed by bonding base boards of 0.6 mm together. A read-only type DVD includes two types of DVDs. As disclosed in Japanese Patent Application Laid-Open No. hei 8-235641, one of them is a DVD that two base boards having recording surfaces are bonded together to use both the surfaces as signal recording surfaces. The other of them is a DVD that a base board having a signal recording surface is bonded to a dummy base board having no signal recording surface to use single surface as a signal recording surface.
Further, as the optical disc having a diameter of 120 mm like the compact disc or the DVD, what is called a Blu-ray disc in which one moving picture can be stored with an image quality the same as that of a high definition television is proposed. This Blu-ray Disc has three types of storage capacity of 23.3 Gbytes, 25 Gbytes and 27 Gbytes. The Blu-ray Disc uses a laser beam having the wavelength of 405 nm further shorter than that of the DVD. Further, the Blu-ray Disc has a structure that a recording layer and a reflecting layer are laminated on a disc board having the thickness of 1.1 mm and a transparent cover layer of 0.1 mm is provided on an uppermost layer to assure a tilt margin.
Further, in the optical disc having both the surfaces used as the signal recording surfaces like the above-described DVD, a printing layer for writing information related to the optical disc cannot be provided on the uppermost layer of each surface. Thus, a DVD that a printing layer is provided adjacently to a protective layer of each base board is disclosed in Japanese Patent Application Laid-Open No. hei 9-274738.
As described above, a plurality of kinds of optical discs such as the compact discs, the DVDs, the Blu-ray Discs, etc. are present in a mixed and confused manner. These optical discs respectively have different specifications, so that they cannot be recorded and reproduced by a common recording and reproducing device. That is, a reproducing device for reproducing the DVD or contents data cannot reproduce the Blu-ray Disc. A reproducing device for the Blu-ray Disc cannot reproduce the compact disc or the DVD.